The present invention relates generally to the melting of metal scrap and particularly to the melting of large bales or briquettes of metal scrap in a manner that limits the formation of skim material.
Large bales and briquettes of metal scrap generally behave as solid units when disposed in a molten melting medium, and because the units are usually less dense than the melting medium, the units float in the medium. Such units are comprised of multilayered composites of good conductive, solid particles of fast melting metal, and good insulators, such as metal oxides, paint and/or oil films and air and other gaseous inclusions that generally surround and insulate each particle of metal. Because of the insulating nature of such films and inclusions, the units are slow to melt and fuel is wasted in the melting process. The need therefore in melting large units of scrap material is the removal of the insulating materials in as rapid a manner as possible, the metal then being exposed to and available for rapid melting by the melting medium. Simultaneously, it is desirable to keep the units afloat in the medium so that any paint or organic materials on and in the units are vaporized and given opportunity to undergo combustion. If lacquer, for example, is submerged in molten aluminum, the lacquer tends to oxidize the aluminum, or at least contributes to the oxidation of the bath, which then accumulates in the aluminum and system as skim. The burning of such lacquers and other combustibles therefore greatly reduces the amount of skim produced in a melting system.
U.S. Pat. No. 4,060,408 to Kuhn, issued Nov. 29, 1977, shows a system for melting large units of floating scrap using a "split hearth" arrangement, i.e. an arrangement in which a charging bay and a heating bay occupy an integral structure, the two bays being separated by a partition. Though this system can ablatively remove insulating material in the large units, the process is slow such that a large structure is required to obtain a degree of efficiency and melt rate. Because, however, the structure is large, the velocity of the melting medium dissipates rapidly, resulting in the end, in a reduced ablative capability.
In U.S. Pat. No. 4,286,985 issued to VanLinden et al on Sept. 1, 1981, a melting system is disclosed in which floating scrap material is ingested into a vortex of melting media in a manner that is much more efficient than prior known devices. As will be seen below, such a system, however, is not suitable for melting large briquettes of solid scrap though it can be used in combination with the apparatus of the invention.